Regions outside London severely "lag behind" in 4G coverage, according to a joint report by Which? and network analyst firm OpenSignal.
The State of Mobile Networks report found that although mobile networks are providing super fast LTE services, most areas of the UK are suffering from a lack of availability.
EE, O2, Vodafone and Three were compared in the report, testing for speed and coverage across the UK.
It found that on average EE had the largest 4G network availability, at 64% coverage, while Vodafone came in second at 60%.
O2 came close behind with 59.9%, but Three's network proved to be the worst performer at 43.7% national coverage.
When the report assessed individual regions however, severe shortfalls were found. While London scored 69.7% average 4G availability, some regions were surprisingly low, the worst-off being Wales at 35.4% and south west England at 45.7%.
"In general the four operators performed worse in our tests than they did nationally in the East and West Midlands, East of England, South West, Scotland and particularly in Wales, where we measured the lowest levels of 4G availability," the report stated.
In five of the 12 regions tested by the report, connection attempts failed at least half the time.
It's clear that UK network providers have noticed this shortfall. EE is currently performing a capacity upgrade on its LTE network, which it believes will boost speeds by 50%, and has vowed to provide 95% of the UK with 4G by 2020.
In a statement to the BBC, Vodafone responded to the report saying: "Thanks to our 2 billion investment in our network and services since 2014, with another 2 billion expected over the next three years, our customers across the country are experiencing a significantly improving network every day."
However the report argued that a lot still needs to be done, stating: "What the UK really needs is a big boost in 4G availability so consumers can take advantage of those speedy connections."
The publication of the findings follows an open letter Three, TalkTalk and others sent to Ofcom demanding a 30% cap on spectrum ownership, to make more spectrum available to smaller mobile operators.
